Write-locking VMAs before isolating them ensures that page fault
handlers don't operate on isolated VMAs.
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
mm/mmap.c | 1 +
mm/nommu.c | 5 +++++
2 files changed, 6 insertions(+)
diff --git a/mm/mmap.c b/mm/mmap.c
index 1f42b9a52b9b..f7ed357056c4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
static inline int munmap_sidetree(struct vm_area_struct *vma,
struct ma_state *mas_detach)
{
+ vma_start_write(vma);
mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
return -ENOMEM;
diff --git a/mm/nommu.c b/mm/nommu.c
index 57ba243c6a37..2ab162d773e2 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
current->pid);
return -ENOMEM;
}
+ vma_start_write(vma);
cleanup_vma_from_mm(vma);
/* remove from the MM's tree and list */
@@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
*/
mmap_write_lock(mm);
for_each_vma(vmi, vma) {
+ /*
+ * No need to lock VMA because this is the only mm user and no
+ * page fault handled can race with it.
+ */
cleanup_vma_from_mm(vma);
delete_vma(mm, vma);
cond_resched();
--
2.39.2.722.g9855ee24e9-googOn Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> Write-locking VMAs before isolating them ensures that page fault
> handlers don't operate on isolated VMAs.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> mm/mmap.c | 1 +
> mm/nommu.c | 5 +++++
> 2 files changed, 6 insertions(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 1f42b9a52b9b..f7ed357056c4 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> static inline int munmap_sidetree(struct vm_area_struct *vma,
> struct ma_state *mas_detach)
> {
> + vma_start_write(vma);
> mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
I may be missing something, but have few questions:
1) Why does a writer need to both write-lock a VMA and mark the VMA detached
when unmapping it, isn't it enough to just only write-lock a VMA?
2) as VMAs that are going to be removed are already locked in vma_prepare(),
so I think this hunk could be dropped?
> if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> return -ENOMEM;
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 57ba243c6a37..2ab162d773e2 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> current->pid);
> return -ENOMEM;
> }
> + vma_start_write(vma);
> cleanup_vma_from_mm(vma);
3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
Thanks,
Hyeonggon
>
> /* remove from the MM's tree and list */
> @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> */
> mmap_write_lock(mm);
> for_each_vma(vmi, vma) {
> + /*
> + * No need to lock VMA because this is the only mm user and no
> + * page fault handled can race with it.
> + */
> cleanup_vma_from_mm(vma);
> delete_vma(mm, vma);
> cond_resched();
> --
> 2.39.2.722.g9855ee24e9-goog
>
>
On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > Write-locking VMAs before isolating them ensures that page fault
> > handlers don't operate on isolated VMAs.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> > mm/mmap.c | 1 +
> > mm/nommu.c | 5 +++++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 1f42b9a52b9b..f7ed357056c4 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > struct ma_state *mas_detach)
> > {
> > + vma_start_write(vma);
> > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
>
> I may be missing something, but have few questions:
>
> 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> when unmapping it, isn't it enough to just only write-lock a VMA?
>
> 2) as VMAs that are going to be removed are already locked in vma_prepare(),
> so I think this hunk could be dropped?
After sending this just realized that I did not consider simple munmap case :)
But I still think 1) and 3) are valid question.
>
> > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> > return -ENOMEM;
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index 57ba243c6a37..2ab162d773e2 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> > current->pid);
> > return -ENOMEM;
> > }
> > + vma_start_write(vma);
> > cleanup_vma_from_mm(vma);
>
> 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
>
> Thanks,
> Hyeonggon
>
> >
> > /* remove from the MM's tree and list */
> > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> > */
> > mmap_write_lock(mm);
> > for_each_vma(vmi, vma) {
> > + /*
> > + * No need to lock VMA because this is the only mm user and no
> > + * page fault handled can race with it.
> > + */
> > cleanup_vma_from_mm(vma);
> > delete_vma(mm, vma);
> > cond_resched();
> > --
> > 2.39.2.722.g9855ee24e9-goog
> >
> >
>
On Tue, Feb 28, 2023 at 11:57 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
>
> On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > > Write-locking VMAs before isolating them ensures that page fault
> > > handlers don't operate on isolated VMAs.
> > >
> > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > ---
> > > mm/mmap.c | 1 +
> > > mm/nommu.c | 5 +++++
> > > 2 files changed, 6 insertions(+)
> > >
> > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > index 1f42b9a52b9b..f7ed357056c4 100644
> > > --- a/mm/mmap.c
> > > +++ b/mm/mmap.c
> > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > > struct ma_state *mas_detach)
> > > {
> > > + vma_start_write(vma);
> > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
> >
> > I may be missing something, but have few questions:
> >
> > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> > when unmapping it, isn't it enough to just only write-lock a VMA?
We need to mark the VMA detached to avoid handling page fault in a
detached VMA. The possible scenario is:
lock_vma_under_rcu
vma = mas_walk(&mas)
munmap_sidetree
vma_start_write(vma)
mas_store_gfp() // remove VMA from the tree
vma_end_write_all()
vma_start_read(vma)
// we locked the VMA but it is not part of the tree anymore.
So, marking the VMA locked before vma_end_write_all() and checking
vma->detached after vma_start_read() helps us avoid handling faults in
the detached VMA.
> >
> > 2) as VMAs that are going to be removed are already locked in vma_prepare(),
> > so I think this hunk could be dropped?
>
> After sending this just realized that I did not consider simple munmap case :)
> But I still think 1) and 3) are valid question.
>
> >
> > > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> > > return -ENOMEM;
> > > diff --git a/mm/nommu.c b/mm/nommu.c
> > > index 57ba243c6a37..2ab162d773e2 100644
> > > --- a/mm/nommu.c
> > > +++ b/mm/nommu.c
> > > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> > > current->pid);
> > > return -ENOMEM;
> > > }
> > > + vma_start_write(vma);
> > > cleanup_vma_from_mm(vma);
> >
> > 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
Ah, yes, you are right. We can safely remove the changes in nommu.c
Andrew, should I post a fixup or you can make the removal directly in
mm-unstable?
Thanks,
Suren.
> >
> > Thanks,
> > Hyeonggon
> >
> > >
> > > /* remove from the MM's tree and list */
> > > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> > > */
> > > mmap_write_lock(mm);
> > > for_each_vma(vmi, vma) {
> > > + /*
> > > + * No need to lock VMA because this is the only mm user and no
> > > + * page fault handled can race with it.
> > > + */
> > > cleanup_vma_from_mm(vma);
> > > delete_vma(mm, vma);
> > > cond_resched();
> > > --
> > > 2.39.2.722.g9855ee24e9-goog
> > >
> > >
> >
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
>
On Wed, Mar 1, 2023 at 10:34 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Tue, Feb 28, 2023 at 11:57 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
> >
> > On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> > > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > > > Write-locking VMAs before isolating them ensures that page fault
> > > > handlers don't operate on isolated VMAs.
> > > >
> > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > ---
> > > > mm/mmap.c | 1 +
> > > > mm/nommu.c | 5 +++++
> > > > 2 files changed, 6 insertions(+)
> > > >
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index 1f42b9a52b9b..f7ed357056c4 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > > > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > > > struct ma_state *mas_detach)
> > > > {
> > > > + vma_start_write(vma);
> > > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
> > >
> > > I may be missing something, but have few questions:
> > >
> > > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> > > when unmapping it, isn't it enough to just only write-lock a VMA?
>
> We need to mark the VMA detached to avoid handling page fault in a
> detached VMA. The possible scenario is:
>
> lock_vma_under_rcu
> vma = mas_walk(&mas)
> munmap_sidetree
> vma_start_write(vma)
>
> mas_store_gfp() // remove VMA from the tree
> vma_end_write_all()
> vma_start_read(vma)
> // we locked the VMA but it is not part of the tree anymore.
>
> So, marking the VMA locked before vma_end_write_all() and checking
> vma->detached after vma_start_read() helps us avoid handling faults in
> the detached VMA.
>
>
> > >
> > > 2) as VMAs that are going to be removed are already locked in vma_prepare(),
> > > so I think this hunk could be dropped?
> >
> > After sending this just realized that I did not consider simple munmap case :)
> > But I still think 1) and 3) are valid question.
> >
> > >
> > > > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> > > > return -ENOMEM;
> > > > diff --git a/mm/nommu.c b/mm/nommu.c
> > > > index 57ba243c6a37..2ab162d773e2 100644
> > > > --- a/mm/nommu.c
> > > > +++ b/mm/nommu.c
> > > > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> > > > current->pid);
> > > > return -ENOMEM;
> > > > }
> > > > + vma_start_write(vma);
> > > > cleanup_vma_from_mm(vma);
> > >
> > > 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
>
> Ah, yes, you are right. We can safely remove the changes in nommu.c
> Andrew, should I post a fixup or you can make the removal directly in
> mm-unstable?
I went ahead and posted the fixup for this at:
https://lore.kernel.org/all/20230301190457.1498985-1-surenb@google.com/
> Thanks,
> Suren.
>
> > >
> > > Thanks,
> > > Hyeonggon
> > >
> > > >
> > > > /* remove from the MM's tree and list */
> > > > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> > > > */
> > > > mmap_write_lock(mm);
> > > > for_each_vma(vmi, vma) {
> > > > + /*
> > > > + * No need to lock VMA because this is the only mm user and no
> > > > + * page fault handled can race with it.
> > > > + */
> > > > cleanup_vma_from_mm(vma);
> > > > delete_vma(mm, vma);
> > > > cond_resched();
> > > > --
> > > > 2.39.2.722.g9855ee24e9-goog
> > > >
> > > >
> > >
> >
> > --
> > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
> >
On Wed, Mar 1, 2023 at 10:34 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Tue, Feb 28, 2023 at 11:57 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
> >
> > On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> > > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > > > Write-locking VMAs before isolating them ensures that page fault
> > > > handlers don't operate on isolated VMAs.
> > > >
> > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > ---
> > > > mm/mmap.c | 1 +
> > > > mm/nommu.c | 5 +++++
> > > > 2 files changed, 6 insertions(+)
> > > >
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index 1f42b9a52b9b..f7ed357056c4 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > > > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > > > struct ma_state *mas_detach)
> > > > {
> > > > + vma_start_write(vma);
> > > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
> > >
> > > I may be missing something, but have few questions:
> > >
> > > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> > > when unmapping it, isn't it enough to just only write-lock a VMA?
>
> We need to mark the VMA detached to avoid handling page fault in a
> detached VMA. The possible scenario is:
>
> lock_vma_under_rcu
> vma = mas_walk(&mas)
> munmap_sidetree
> vma_start_write(vma)
>
> mas_store_gfp() // remove VMA from the tree
> vma_end_write_all()
> vma_start_read(vma)
> // we locked the VMA but it is not part of the tree anymore.
>
> So, marking the VMA locked before vma_end_write_all() and checking
Sorry, I should have said "marking the VMA *detached* before
vma_end_write_all() and checking vma->detached after vma_start_read()
helps us avoid handling faults in the detached VMA."
> vma->detached after vma_start_read() helps us avoid handling faults in
> the detached VMA.
>
>
> > >
> > > 2) as VMAs that are going to be removed are already locked in vma_prepare(),
> > > so I think this hunk could be dropped?
> >
> > After sending this just realized that I did not consider simple munmap case :)
> > But I still think 1) and 3) are valid question.
> >
> > >
> > > > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> > > > return -ENOMEM;
> > > > diff --git a/mm/nommu.c b/mm/nommu.c
> > > > index 57ba243c6a37..2ab162d773e2 100644
> > > > --- a/mm/nommu.c
> > > > +++ b/mm/nommu.c
> > > > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> > > > current->pid);
> > > > return -ENOMEM;
> > > > }
> > > > + vma_start_write(vma);
> > > > cleanup_vma_from_mm(vma);
> > >
> > > 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
>
> Ah, yes, you are right. We can safely remove the changes in nommu.c
> Andrew, should I post a fixup or you can make the removal directly in
> mm-unstable?
> Thanks,
> Suren.
>
> > >
> > > Thanks,
> > > Hyeonggon
> > >
> > > >
> > > > /* remove from the MM's tree and list */
> > > > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> > > > */
> > > > mmap_write_lock(mm);
> > > > for_each_vma(vmi, vma) {
> > > > + /*
> > > > + * No need to lock VMA because this is the only mm user and no
> > > > + * page fault handled can race with it.
> > > > + */
> > > > cleanup_vma_from_mm(vma);
> > > > delete_vma(mm, vma);
> > > > cond_resched();
> > > > --
> > > > 2.39.2.722.g9855ee24e9-goog
> > > >
> > > >
> > >
> >
> > --
> > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
> >
On Wed, Mar 01, 2023 at 10:42:48AM -0800, Suren Baghdasaryan wrote:
> On Wed, Mar 1, 2023 at 10:34 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > On Tue, Feb 28, 2023 at 11:57 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
> > >
> > > On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> > > > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > > > > Write-locking VMAs before isolating them ensures that page fault
> > > > > handlers don't operate on isolated VMAs.
> > > > >
> > > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > > ---
> > > > > mm/mmap.c | 1 +
> > > > > mm/nommu.c | 5 +++++
> > > > > 2 files changed, 6 insertions(+)
> > > > >
> > > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > > index 1f42b9a52b9b..f7ed357056c4 100644
> > > > > --- a/mm/mmap.c
> > > > > +++ b/mm/mmap.c
> > > > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > > > > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > > > > struct ma_state *mas_detach)
> > > > > {
> > > > > + vma_start_write(vma);
> > > > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
> > > >
> > > > I may be missing something, but have few questions:
> > > >
> > > > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> > > > when unmapping it, isn't it enough to just only write-lock a VMA?
> >
> > We need to mark the VMA detached to avoid handling page fault in a
> > detached VMA. The possible scenario is:
> >
> > lock_vma_under_rcu
> > vma = mas_walk(&mas)
> > munmap_sidetree
> > vma_start_write(vma)
> >
> > mas_store_gfp() // remove VMA from the tree
> > vma_end_write_all()
> > vma_start_read(vma)
> > // we locked the VMA but it is not part of the tree anymore.
> >
> > So, marking the VMA locked before vma_end_write_all() and checking
>
> Sorry, I should have said "marking the VMA *detached* before
> vma_end_write_all() and checking vma->detached after vma_start_read()
> helps us avoid handling faults in the detached VMA."
>
> > vma->detached after vma_start_read() helps us avoid handling faults in
> > the detached VMA.
Thank you for explanation, that makes sense!
By the way, if there are no 32bit users of Per-VMA lock (are there?),
"detached" bool could be a VMA flag (i.e. making it depend on 64BIT
and selecting ARCH_USES_HIGH_VMA_FLAGS)
Thanks,
Hyeonggon
On Wed, Mar 1, 2023 at 4:54 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
>
> On Wed, Mar 01, 2023 at 10:42:48AM -0800, Suren Baghdasaryan wrote:
> > On Wed, Mar 1, 2023 at 10:34 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > >
> > > On Tue, Feb 28, 2023 at 11:57 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
> > > >
> > > > On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> > > > > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > > > > > Write-locking VMAs before isolating them ensures that page fault
> > > > > > handlers don't operate on isolated VMAs.
> > > > > >
> > > > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > > > ---
> > > > > > mm/mmap.c | 1 +
> > > > > > mm/nommu.c | 5 +++++
> > > > > > 2 files changed, 6 insertions(+)
> > > > > >
> > > > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > > > index 1f42b9a52b9b..f7ed357056c4 100644
> > > > > > --- a/mm/mmap.c
> > > > > > +++ b/mm/mmap.c
> > > > > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > > > > > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > > > > > struct ma_state *mas_detach)
> > > > > > {
> > > > > > + vma_start_write(vma);
> > > > > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
> > > > >
> > > > > I may be missing something, but have few questions:
> > > > >
> > > > > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> > > > > when unmapping it, isn't it enough to just only write-lock a VMA?
> > >
> > > We need to mark the VMA detached to avoid handling page fault in a
> > > detached VMA. The possible scenario is:
> > >
> > > lock_vma_under_rcu
> > > vma = mas_walk(&mas)
> > > munmap_sidetree
> > > vma_start_write(vma)
> > >
> > > mas_store_gfp() // remove VMA from the tree
> > > vma_end_write_all()
> > > vma_start_read(vma)
> > > // we locked the VMA but it is not part of the tree anymore.
> > >
> > > So, marking the VMA locked before vma_end_write_all() and checking
> >
> > Sorry, I should have said "marking the VMA *detached* before
> > vma_end_write_all() and checking vma->detached after vma_start_read()
> > helps us avoid handling faults in the detached VMA."
> >
> > > vma->detached after vma_start_read() helps us avoid handling faults in
> > > the detached VMA.
>
> Thank you for explanation, that makes sense!
>
> By the way, if there are no 32bit users of Per-VMA lock (are there?),
> "detached" bool could be a VMA flag (i.e. making it depend on 64BIT
> and selecting ARCH_USES_HIGH_VMA_FLAGS)
Yeah, I thought about it but didn't want to make assumptions about
potential users just yet. Besides, I heard there are attempts to make
vm_flags to be always 64-bit (I think Matthew mentioned that to me
once). If that happens, we won't need any dependencies here. Either
way, this conversion into a flag can be done as an additional
optimization later on. I prefer to keep the main patchset as simple as
possible for now.
Thanks,
Suren.
>
> Thanks,
> Hyeonggon
>
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